The present invention generally relates to an apparatus and method for clamping a semiconductor mask during the process by which a high resolution pattern is scribed on the mask.
It is well known in the semiconductor wafer manufacturing art that so-called xe2x80x9cmasksxe2x80x9d are used in connection with semiconductor wafer processing. In connection with such processing, a given wafer is subjected to many steps, during which masks are used to establish various patterns on the many layers of the wafer as it is progressively coated with the insulative and conductive materials, which eventually form the complex circuitry on the extremely tiny chips that are eventually diced out of the total wafer. Such masks are typically made of glass.
Before a given mask can be used for such wafer processing, the mask, itself, must be subjected to a process by which the high resolution patterns are scribed onto its surface, wherein the scribing is generally done with a laser or an electron beam (e-beam). In a typical mask scribing operation, the mask is first loaded onto a carrier device, and the carrier device containing the mask is then placed under the automated control of the laser or e-beam machine that performs the scribing process. During this process the carrier and the mask are subjected to the very rapid movements of the machine. One concern that results from this processing approach is that the rapid acceleration and deceleration of the carrier and the mask, during the mask scribing process, may cause the mask to shift its position on the carrier. As can easily be appreciated, the very precise alignment and positioning of the mask on the carrier is critical since its positioning will determine where the laser or e-beam will actually scribe the pattern. Hence, it is very important that the clamp be powerful enough to hold the mask firmly and fixedly in place during the entire scribing operation, which necessarily means that the mask cannot shift position relative to the carrier device as the two of them are rapidly moved about by the machine. On the other hand, the clamp cannot place an excessive force on the glass mask, since an excessive force could generate stress fields within the glass that might degrade the mask or the performance of the scribing process. Additionally, in order to make the clamp usable in the very small amount of space that is available in a laser scribing chamber, it is desirable for the clamp to be physically as small as possible, or to have a minimal xe2x80x9cfootprintxe2x80x9d. Thus, the clamping mechanism used to hold the mask in place during the scribing operation must have a compact size, and must serve the dual purposes of maintaining the mask in a fixed position relative to the carrier, and doing so in a manner that does not damage the mask.
In addition to physically securing the mask, the mask clamp must be able to hold the mask perfectly level (or xe2x80x9cplanarizedxe2x80x9d) during the scribing process. With respect to modern scribing systems, such planarization must be done to extremely tight tolerances, typically at the sub-tenth micron level. Accordingly, the clamp must be able to allow for the adjustment of the height and angle of the surface of the mask, so that it can be made perfectly level to accommodate the precise scribing process. Yet another concern arises from the use of scribing tools, such as e-beam lithography tools, which may generate charges on the mask during the scribing process. As a result, the clamp must be able to conduct any such charges away from the mask to prevent electric field generation which may cause the mispositioning of the scribing beam. Care must also be taken to not generate magnetic fields introduced by magnetic or conductive materials which may produce eddy currents.
Moreover, for various reasons of convenience and manufacturing efficiency, it is desirable to have a clamp that is easy to load with the mask, both manually and through automation, and requires a minimal number of steps to operate. More particularly, certain known clamps are activated from underneath or by turning mechanisms from the side. Such approaches are not particularly easy to use, especially in connection with automated loading of a mask in the clamp.
Accordingly, what is needed is a clamping device which addresses the various concerns noted above.
In accordance with the preferred embodiment of the present invention, an apparatus and method for clamping a semiconductor mask to a carrier device is provided. The mask clamp includes a base, to which is attached a spring. Mounted on the spring is a ball that makes contact with the underside of the mask when it is mounted in the clamp. Directly and precisely opposed to the ball which makes contact with the underside of the mask, is a another ball mounted in the top portion of the clamp, and which involves contact with the top side of the mask. Accordingly, when the spring is depressed, there is sufficient space for the mask to be mounted in the clamp, but when the spring is released, the mask is fixedly pinched between the two balls. In addition, the top portion of the clamp is adjustable by means of a high resolution height adjustment screw. The adjustment screw allows for very precise adjustments to the height of the mask once it is in place in the clamp, and therefore can be used to planarize the top surface of the mask. Finally, in one alternate embodiment, the clamp includes grounding contacts, which make electrical contact with the mask when it is in position. In this manner, the clamp can be used to maintain the mask at a constant electrical potential, such as a ground potential, during the scribing of the pattern on the mask.
It is therefore an object of the present invention to provide an apparatus and method for clamping a semiconductor mask on a carrier for the overall purpose of scribing the mask with a high resolution pattern.
It is also an object of the invention to provide such an apparatus and method for keeping the mask in a fixed position relative to the carrier during the rapid movement that the mask and carrier are subjected to during the scribing process.
It is another object of the invention to provide such an apparatus that can precisely adjust the height and surface angle of the mask so that it can be planarized within extremely refined tolerances.
It is yet a further object of the invention to provide such an apparatus and method that meets the electrical and magnetic requirements and limitations for use in the scribing process.
It is still further an object of the invention to provide such an apparatus and method that has a small geometric profile, is powerful in spite of its small size, and is easy to use in connection with manual as well as automated loading of the mask.